Go here for detailed instructions on changing the water pump:
First off, it's a job to change the waterpump & timing belt.
Disconnect the battery,
Remove serpentine belt & A/C belt,
raise vehicle & support it on jackstands,
crawl under the van & remove all but the last powersteering bracket bolts. The last one will be closest to the center of the engine, loosen it about 3 turns, but enough threads engaged that the bracket can move, but not completely come off.
Go to the front of the vehicle & remove the A/C compressor from the bracket, then remove the bracket.
You can now remove the lower plastic cover in the passenger side wheelwell, that goes up toward the front of the valance. You have to remove the tire there to get at the crankshaft pulley, but no need to remove it yet. We will get to it soon enough.
Now lower the vehicle back down on the tires,
remove the upper radiator hose after draining the radiator of coolant,
remove the motor mount on the passenger side upper fender. To remove it, you need to support the engine with a jack & a block of wood under the oil pan. Just raise the engine enough to take tension off the bolts.
Now with the upper motor mount removed, you can get to the motor plate, remove the bolts holding it to the front of the engine,
Go to the passenger side wheelwell, remove the crankshaft pully & oil slinger. The harmonic balancer slides right off, no puller necessary,
Take off the bolts holding the plastic cover over the timing belt & water pump.
Make sure the timing marks are lined up the way the link (listed above) shows you,
Using a pry bar, push the tensioner out of the way & tighten the bolt that holds tensioner so it's out of the way. Remove the belt.
Remove the bolts holding the waterpump to the engine, clean up the surfaces of the engine where the water pump bolts to.
I like to use RTV silicone sealant on the waterpump side of the gasket surface to hold the gasket in place. Put it aside & let it dry. Coat the engine side of the gasket with RTV to ensure no leaks later on. Let it dry.
Replace the "O" ring on the pipe going into the back of the waterpump. Make sure to lube it with an approve lube that will allow the "O" ring to slide into place. Don't want any leaks here either.
On my 3.0 Ltr engine I had to put the timing belt on with everything lined up, then rotate the rear cam counterclockwise (without rotating the front cam or crankshaft) about 1.5 cogs on the timing belt. Then apply tension using the spring load on the tensioner. It should rotate the rear cam clockwise to the appropriate timing mark. Before anything else happens, make sure the timing belt tensioner is putting tension on the timing belt & the timing marks line up. If they do, I like to rotate the engine 4 complete cycles just to make sure the timing marks line up. If they don't it's a heck of a lot easier to fix now.
Once you are confident the waterpump is torqued on, the timing marks line up with the marks on the engine, put on the plastic cover over the waterpump & timing belt.
Re-assemble the front of the engine in reverse order of the disassembly. Be sure to put the tire/wheel back on, lower the van off the jack stands & everything has been reinstalled.
Hook up the battery, fill the radiator with coolant, start it up. Top off the coolant as needed as the engine warms.
That's all there is to it. Took me 3 days, but I took my time doing it in the garage, did it right. The 2 biggest challenges were
1. Taking the front motor plate off - no instructions to remove the bolts holding the power steering bracket or remove the A/C compressor bracket - and......
2. Getting the Overhead Cam's to line up with the timing marks. When putting tension on the timing belt one of the two cams or the crank will rotate, if not held in position. It's awful easy to get the cams one cog off. If it does that, just stop & think which direction the cam has to move to line everything up. It's easy to fix when you have it all apart.